1. Field of the Invention
This invention relates to a composite orthopedic implant having a low friction material substrate with primary frictional features and secondary frictional features.
2. Description of the Related Art
The placement of spinal implants between vertebrae is a common surgical procedure. A number of such spinal implants, which are generally hollow and box-shaped or cylindrical, have been developed. One risk of such procedures is the post-operative expulsion or dislocation of the implanted device. There is a need to increase the frictional forces between the device and the bone surface.
The most advantageous material for the manufacture of intervertebral spinal implants is thermoplastic polymer, of which the most commonly used is polyetheretherketone (PEEK). This material has proven biocompatibility with human tissue and is biomechanically strong enough to withstand long-term cyclical loading as occurs within the spine. This type of material has a modulus of elasticity similar to bone, reducing the probability of bone subsidence which can occur with harder metallic implants. A significant problem, however, with the use of such polymeric spinal implants is inherent low levels of bone-device surface interaction. Machined or molded polymeric materials tend to have relatively high levels of lubricity, elasticity, and smoothness which conspire to reduce friction at the bone-device interface. This can result in undesirably low frictional forces between bone and the implanted device. Several parties have attempted to address this issue by adding large frictional features to the polymer implant. These features are typically exemplified by surface teeth of various designs. Although surface teeth increase interface friction somewhat, the underlying challenges of lubricity, smoothness and elasticity remain.
What is needed, therefore, is a polymer implant that builds upon the current state of the art.